March 28, 2016
2 min read

Two-dose varicella vaccine more effective than one dose

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Recent findings published in Pediatrics suggested that the two-dose varicella vaccine was more effective than the single-dose vaccine.

“During the first 5 years after implementation of the two-dose varicella vaccination program, we found that two doses conferred significantly better protection against varicella disease from community transmission among school-aged children compared with the one-dose regimen,” Dana Perella, MPH, surveillance coordinator at the Philadelphia Department of Public Health, and colleagues wrote. “Our study provides more direct evidence of the protective effect of a two-dose regimen of varicella vaccine for children.”

Between 2001 and 2006, varicella outbreaks persisted in schools with greater than 80% single-dose coverage, the researchers wrote. During this time, clinical trials showed that the two-dose vaccine created an immune response 12-times greater than the single-dose after 6 weeks. In 2006, the Advisory Committee on Immunization Practices recommended the two-dose vaccine for children aged 4 to 6 years. By 2012, 36 states had a two-dose varicella vaccination requirement for elementary school students, but its true effectiveness has been difficult to estimate due to lower varicella incidence.

To determine the overall and incremental effectiveness of the two-dose varicella vaccine, the researchers performed a matched case-control study of children diagnosed with varicella (n = 125) and controls (n = 408) at two surveillance sites from 2009 to 2011. The researchers compared patients (aged 0 to 18 years) who received either the single-dose vaccine or those (aged 4 to 18 years) who received the two-dose vaccine with patients who received neither vaccine.

The researchers found that the single-dose vaccine was 75.6% effective (95% CI, 38.7-90.3) in preventing any varicella and 78.1% effective (95% CI, 12.7-94.5) in preventing moderate or severe varicella, defined as at least 50 lesions. Efficacy for the two-dose vaccine was 93.6% (95% CI, 75.6-98.3) against any varicella and 97.9% (95% CI, 83-99.7) against moderate or severe varicella. Incremental effectiveness of the two-dose vs. single dose vaccine was 87.5% against clinically diagnosed disease and 97.3% against laboratory-confirmed varicella.

Because breakthrough varicella has only a few vesicular lesions and is difficult to diagnose, the researchers wrote, they examined it by using two case definitions: one based on clinical and epidemiologic criteria, and the other on laboratory confirmation. Both definitions produced similar effectiveness estimates regardless of single or double doses.

“With superior protection provided by the two-dose varicella vaccination compared with the one-dose regimen as demonstrated in our study and others, it will be important to expand school immunization requirements to include two-dose varicella vaccination,” Perella and colleagues wrote. “Catch-up varicella vaccination will be particularly important for one-dose vaccinees at increased risk for exposure to people with varicella or herpes zoster.” – by Will Offit

Disclosure: The researchers report no relevant financial disclosures.